It is known that a pair of eyeglasses comprises two lenses that may be ophthalmic correcting lenses and/or sunglass lenses that are fitted to a frame which is designed to be placed on the wearer's nose in such a manner as to position one lens appropriately in front of each eye. Usually, the lenses are fixed permanently to the frame in a mounting operation.
There exist several ways of mounting ophthalmic lenses. There are thus frames with rimmed lenses in which the frame typically comprises rims having the peripheral edges of the lenses fitted in edge-on after being cut out to the corresponding shape.
There are also mounts using pierced lenses with wire frames that do not have rims, with the lenses being secured thereto at certain points by bolting. Typically, each lens presents two laterally-opposite through holes, one for securing to the corresponding end of the bridge, and the other to the hinge of the arm or “temple” that is associated therewith. Fastening is then provided by bolts or the like passing through the lens via the holes made in this way. In order to prevent the lens from pivoting in unwanted manner about the fastening bolts, a notch opening out to the edge of the lens is generally provided in the vicinity of each hole, and a finger is engaged in the notch to prevent turning.
Although those traditional mounting techniques generally give satisfaction from the point of view of positioning lenses accurately in front of the eye, they nevertheless present the major drawback of requiring a relatively difficult special operation to be performed by qualified operatives using relatively expensive special tooling. Furthermore, mounting performed in that way is permanent and a lens can be replaced only by performing an operation that is just as complex and that lies outside the normal ability of a wearer of eyeglasses not specialized in the assembly thereof.
As a result, the cost of fitting and replacing lenses is relatively high. However, there exists a need for inexpensive eyeglasses that can be assembled quickly, and also for lenses and frames to be interchangeable. Such a need for quick assembly and/or disassembly is felt more particularly under the following circumstances:                providing equipment in poor countries where there is a shortage of qualified personnel and a desire to provide the population with eyeglasses at low cost;        wearers of eyeglasses desirous of having several pairs available at low cost; and        wearers of eyeglasses interested in modularity, with lenses and frames being interchangeable as a function of their activities, the seasons, fashion, rapid changes to their eyesight, etc.        
U.S. Pat. No. 6,059,409 provides a first answer to this expectation. It describes a pair of eyeglasses having clipped (or clamped) lenses that can be interchanged quickly. In those eyeglasses, the lenses are clipped transversely: the frame possesses studs that are elastically flexible transversely, i.e. in the plane of the lens, and that are suitable for co-operating with notches formed in the edge face of the lens. The major drawback of that solution lies in the radial nature of the elastic clamping performed, since in order to hold the lens effectively it needs to be associated with the lens being surrounded in part by a rim, thus making the frame as a whole relatively bulky and unattractive in appearance.
U.S. Pat. No. 3,471,222 (Eisler) describes half-glasses in which the lenses are fitted to the frame by their bottom edges being received in corresponding grooves in partial rims of the frames, after going past an end hard point. However the clamping force exerted by the partial rims on the lenses is essentially radial and not axial as specified by claim 1 of the present application. Like the preceding solution, the frame proposed in that way is unattractive and/or restricted to half-glasses, insofar as it is ill-suited to mounting lenses of larger size.
U.S. Pat. No. 3,709,587 describes a pair of eyeglasses in which the lenses are clipped to the frame by means of protuberances formed at the peripheries of the lenses and engaged in clamped manner in corresponding sockets in the frame. Two embodiments are envisaged.
In the first embodiment, shown in FIG. 1 of that document, the frame possesses its own cohesion independently of the lenses, with small horizontal strips connecting the bridge to the temples. Each lens is fitted to the corresponding strip by means of a protuberance formed in the bottom portion of each lens in order to be fitted into a corresponding socket in the strip. Nothing is said about how the fitting is performed; in any event the fitting zone is unique for each lens, which makes mounting awkward to perform and not very reliable, in particular because of a lack of stability and rigidity.
In the second embodiment shown in FIG. 12 of that patent, each lens is provided with two diametrically-opposite side studs that are engaged in corresponding notches of the frame. However the frame is made up of three separate portions: a bridge for the nose and two temples, without any rim or strip providing a connection between the bridge and the temple. Overall cohesion is provided by the lenses, which themselves provide the junction between the bridge and the temple. That structure for eyeglasses is lacking in rigidity, in particular when the lens and the frame constituted solely by the temples and the bridge are all made of plastics material. In addition the assembly is difficult to put together and can require the use of adhesive, which is unattractive in appearance and inconvenient.